Chemiluminescence spectra have been recorded for low-pressure, highly dilute, fuel-lean atomic oxygen flames of C2H2 and C3O2; under typical flame conditions the total pressure was 0.83 Torr with 1.1 mTorr of O atoms, 0.44 mTorr of O-2, 0.20 mTorr of fuel, and the balance Ar. Spectral coverage was complete from 183 to 1500 nm for C2H2, and from 183 to 885 nm for C3O2 Strong CO a --> X Cameron band emission was found to be the dominant feature of the chemiluminescence signature from 190 to 260 nm for C2H2 oxidation under these conditions, with distinct but relatively minor CO A --> X fourth positive emission between 185 and 195 nm. There is strong emission from higher tripler states of CO throughout the visible and near-IR, with CO e --> a, d --> a, and a’ --> a emission features observed. Nearly identical CO emission spectra were obtained for both C2H2 and C3O2 fuels, which indicates that for both fuels the source of electronically excited CO is the C2O + O reaction. Quantification of emission yields for the four triplet electronic states of CO observed here indicates that little or no CO(a) is formed directly, rather its population results from radiative emission from higher triplet states. Approximately 70% of the triplet CO formed directly from the C2O + O reaction is in the a’ state, which had not been previously identified in this system.